class Solution {
    public int uniquePaths(int m, int n) {
        int dp[] = new int[n];
        Arrays.fill(dp, 1);

        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                dp[j] += dp[j-1];
            }
        }

        return dp[n-1];
    }
}